When you're designing a product, you need to have some real live scenarios in mind for how people are going to use it. Otherwise you end up designing a product that doesn't correspond to any real-world usage (like the Cue?Cat).
This template is taken from - joelonsoftware.com
Pick your product's audiences and imagine a fictitious, totally imaginary but totally stereotypical user from each audience who uses the product in a totally typical way. Chapter 9 of my UI design book (available online for free) talks about creating fictional users and scenarios. This is where you put them - joelonsoftware.com
The more vivid and realistic the scenario, the better a job you will do designing a product for your real or imagined users, which is why I tend to put in lots of made-up details.